1. Field of the Invention
The present invention relates to a method, apparatus, and program for driving a motor, and more particularly to a method, apparatus, and program for driving a motor in a feedback control system.
2. Discussion of the Background
Stepping motors are widely used in diverse applications requiring accurate positioning or drive control, such as image forming apparatuses, cameras, automobiles, etc. With the stepping motor, positioning or driving of an object can be easily and accurately controlled by using a feedback control system.
For example, such a feedback control system generally includes a stepping motor, an object to be controlled, a detector, and a controller. The stepping motor drives the object. The detector detects the speed of the object. To control the object to have a desired speed, the controller calculates a control value, based on the difference between the detected speed and the desired speed of the object, generates a drive current or voltage based on the control value, and applies the drive current or voltage to the stepping motor. With this drive current or voltage, the stepping motor makes a stepwise rotation so as to drive the object at the desired speed.
One drawback of this feedback control system is that the stepping motor tends to oscillate when a large control value is generated, since it instantaneously changes a drive current or voltage. To solve this problem, microstep drive is generally applied, which divides one full-step into a number of smaller steps, called microsteps. More specifically, a drive current or voltage of a sinusoidal waveform is divided into a number of stepped currents or voltages having different levels, and the stepped drive currents or voltages are fed to the respective windings with phase differences between them. With this technique, the stepping motor tends to rotate more smoothly. However, oscillation is still observed in some cases.
In one example, oscillation is observed when more than two different excitation modes are used in one feedback control system. For example, a feedback control system is provided, which drives a stepping motor in two different excitation modes, including 2W1-2 and 4W1-2 phase excitation drive modes. In such a system, a higher control value is generated in the 2W1-2 mode than a control value in the 4W1-2 mode. In other words, the stepping motor, operating in the 2W1-2 mode, becomes too sensitive to the change in speed, and tends to generate oscillation rather than to suppress it.